1. Technical Field
The present invention relates to a method of separating group II nuclides from a radioactive waste lithium chloride salt and recovering pure lithium chloride using lithium oxide.
2. Description of the Related Art
In a pyroprocess of recovering uranium and transuranic (TRU) metals from oxide-type spent nuclear fuel, during the electro-reduction process of converting the oxide-type spent nuclear fuel into metal-type spent nuclear fuel, lithium chloride (LiCl) is used as a high-temperature electrolyte, and lithium chloride (LiCl) waste containing barium (Ba) and strontium (Sr) as radioactive nuclides is discharged. Particularly, since strontium (Sr) is a high-heat generation nuclide, the lithium chloride (LiCl) waste containing strontium (Sr) must be stably processed.
There is a technology for recovering a suitable amount of recyclable lithium chloride (LiCl) from the lithium chloride (LiCl) waste and concentrating barium (Ba) and strontium (Sr) nuclides in lithium chloride (LiCl) [Korean Patent No. 10-2008-0093470, 12/500,869]. However, the Ba and Sr nuclides-concentrated lithium chloride (LiCl) waste discharged by this technology has high solubility in water, cannot be easily solidified, and includes a large amount of high-corrosion lithium chloride (LiCl). Further, since barium (Ba) and strontium (Sr) also exist in the form of chlorides, it is not easy to process this lithium chloride (LiCl) waste.
It was reported in the non-patent documents of the U.S.A that barium (Ba) and strontium (Sr) can be selectively removed from the molten LiCl—KCl salt system using zeolite 4A [Non-patent documents: Michael F. Simpson* and Mary Lou D. Gougar, “Two-Site Equilibrium Model for Ion Exchange between MonovalentCations and Zeolite-A in a Molten Salt”, Ind Eng. Chem. Res. 2003, 42, 4208-4212, R. K. Ahluwalia,* H. K. Geyer, C. Pereira, and J. P. Ackerman, “Modeling of a Zeolite from Molten Salt”, Ind Eng. Chem. Res. 1998, 37, 145-153, Supathom Phongikaroon and Michael F. Simpson, “Equilibrium Model for Ion Exchange Between Multivalent Cations and Zeolite-A in a Molten Salt”, AICHE, 2006, 52(5), 1736-1743, Lexa D., “Occlusion and ion exchange in the molten (lithium chloride potassium chloride to alkaline earth chloride) salt zeolite 4A system with alkaline earth chlorides of calcium and strontium, and in the molten (lithium chloride potassium chloride actinide chloride) salt zeolite 4A system with the actinide chloride of uranium”, Metallurgical and Materials Transactions B. 2003, 34, 201-208]. However, in the LiCl system, the zeolite structure completely breaks down, which means that the ion-exchange performance and occlusion performance of zeolite 4A disappear. Therefore, the ability of zeolite 4A to selectively remove barium (Ba) and strontium (Sr) cannot be used in the LiCl system [“PWR spent nuclear fuel volume reduction technology development (II)”, Korea Atomic Energy Research Institute, KAERI/RR-3132/2009]. Further, when zeolite is used, there is a problem in that a large amount of sodium (Na) is introduced into lithium chloride (LiCl), so that the composition of lithium chloride (LiCl) changes, with the result that it is difficult to recycle this lithium chloride (LiCl).
In order to solve the above problem, there is a method of separating nuclides and recovering LiCl by converting Sr and Ba included in LiCl into sulfates or carbonates thermally stable compared to chlorides using Li2SO4 or Li2CO3 and vaporizing LiCl [Non-patent document, H. C. Eun et al., Study on a separation method of radionuclides (Ba,Sr) from LiCl salt wastes generated from the electroreduction process of spent nuclear fuel, available online, 23 September 2011, JRNC]. However, this method is also disadvantageous in that the finally-produced sulfate-type nuclides do not easily solidify, and the finally-produced carbonate-type nuclides are thermally unstable at the solidification temperature.
Thus, the present inventors have developed methods of recovering renewable LiCl by converting Sr and Ba included in LiCl into easily-solidifiable oxide (or oxychloride) using Li2O and then distilling LiCl at a reduced pressure condition, thus completing the present invention.